The central point or core of something; the part that matters most; can also mean a small lump or knob.
From Low German 'knubbe' meaning knob or lump. The word developed from the physical meaning (a small bump) to the metaphorical meaning (the crux of a matter).
The 'nub' of something is its essential truth—which is why it comes from a word meaning a little lump. Sometimes the truth is small and hard, like a knob!
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